The present invention is related to co-pending application Ser. No. 698,723 "Reinforced Ablative Thermal Barriers" filed on even date hereof by the same applicant. As disclosed in the co-pending application, retention of certain kinds of thermal barriers on the surface of articles to be protected is improved when a folded and extensible member is included within the ablative material. In particular, the adhesion of a silicone rubber type of material to the interior of a cylindrical combustor is improved substantially when a fiber reinforced polymer rib is run helically along the interior of the combustor with a relatively close pitch. The rib is attached to the case by a resin bond and the rubber fills the space between the rib turns.
In the basic concept of the invention, the ribs can be made of any material which does not swell as does the elastomer material. And the material must be sufficiently strong and resistant to thermal degradation to carry out the intended function of holding the swelling material to the surface to be protected. In the preferred practice of the invention the rib is folded or corrugated so that when swelling occurs the rib will tend to elongate radially inward, drawing the rib with it. It is found that the compliance of the rib is particularly effective in retaining the primary protective function of the silicone rubber. The rib is relatively small in its cross sectional area which is exposed to the interior combustor gases. Typically it will be about 0.4-10 mm wide.
The rib runs circumferentially around the interior of the combustor; it may run circularly or helically, with the latter preferred. With a helical combustor, it will be appreciated that the rib and rubber strip contained between adjacent turns both constitute continuous members running in a helical path down the length of the combustor. In either design, one way of making the thermal barrier invention is to prefabricate a rib shape, adhere it to the inside wall of the combustor, and then flow silicone rubber into place and cure it. This approach involves complications in accurately and adequately positioning the rib in place. Thus, the present invention reflects attempts to improve the manufacture of combustors of the type described.